Polyolefins, such as polyethylenes, which have high molecular weight, generally have improved mechanical properties over their lower molecular weight counterparts. However, high molecular weight polyolefins can be difficult to process and can be costly to produce. Polyolefins having a bimodal molecular weight distribution are desirable because they can combine the advantageous mechanical properties of high molecular weight (“HMW”) fraction with the improved processing properties of the low molecular weight (“LMW”) fraction.
There are several methods for producing bimodal or broad molecular weight distribution polyolefins, e.g., melt blending, reactor in series or parallel configuration, or single reactor with bimetallic catalysts. However, melt blending suffers from the disadvantages brought on by the needs of complete homogenization and high cost.
Bimetallic catalysts such as those disclosed in U.S. Pat. Nos. 5,032,562; 5,525,678; and EP 0,729,387, can produce bimodal polyolefins in a single reactor. These catalysts typically include a non-metallocene catalyst component and a metallocene catalyst component which produce polyolefins having different average molecular weights. U.S. Pat. No. 5,525,678, for example, discloses a bimetallic catalyst including a titanium non-metallocene component which produces a HMW fraction, and a zirconium metallocene component which produces a LMW fraction.
As stated in U.S. Pat. No. 6,995,109, controlling the relative amounts of each catalyst in a reactor, or the relative reactivity of the different catalysts, allows control of the bimodal product. Other background references include EP 0,676,418; WO 98/49209; WO 97/35891; and U.S. Pat. No. 5,183,867.
Bimetallic catalysts are also disclosed in, for example, U.S. Pat. Nos. 7,199,072; 7,141,632; 7,172,987; 7,129,302; 6,964,937; 6,956,094; and 6,828,394.
Those non-metallocene catalysts, such as pyridyl amines, have been used to prepare Group 4 complexes which are useful transition metal components for use in the polymerization of olefins, see, for example, US 2002/0142912; U.S. Pat. Nos. 6,900,321; and 6,103,657, where this kind of ligands has been used in complexes in which the ligands are coordinated in a bidentate fashion to the transition metal atom. Another example, U.S. Pat. No. 7,973,116, provides pyridyldiamido transition metal complexes and processes to polymerize olefins using such pyridyldiamido complexes. Other background references include US 2015/141590, US 2014/256893, US 2014/316089, WO 2014/123683, and WO 2013/028283.
It is still desirous to develop bimetallic catalyst systems for the production of bimodal polyolefins in a single reactor to increase commercial usefulness and produce polymers having improved properties.